Background Developing a safe and effective HIV-1 vaccine has been hampered by the inability to design immunogens that can induce antibodies capable of potently neutralizing diverse HIV-1 strains. Despite the recognition of conserved HIV-1 envelope (Env) regions by rare, broadly neutralizing antibodies, these regions fail to induce protective antibodies when used as immunogens or in the context of natural infections. Various hypotheses have been offered to explain the absence of an effective immune response to Env determinants, including the suppression of this response by immunological tolerance. This hypothesis arose from the observation that broadly neutralizing HIV-1 antibodies can cross-react with self-antigens.
Methods To test the tolerance hypothesis, we generated 2F5 VH knock-in mice, in which the immunoglobulin (Ig) heavy chain variable region rearrangement (VHDHJH) of the broadly neutralizing human antibody 2F5 was targeted into the JH cluster of the mouse Igh locus.
Results In vitro, chimeric human/mouse 2F5 antibodies were functionally equivalent to the human 2F5 antibody. In vivo, the 2F5 VH insertion resulted in a profound B cell developmental blockade in the bone marrow with >80% loss of immature B cells. Furthermore, both 2F5 VH+/- and 2F5 VH+/+ mice lacked serum reactivity to cardiolipin and anti-nuclear autoantigens, yet had detectable, albeit severely diminished, mature splenic B cell populations. In 2F5 VH+/- mice, the majority of remaining mature splenic B cells used endogenous heavy chains, indicating loss of effective allelic exclusion.
Summary The 2F5 VH knock-in phenotype identifies a profound effect of tolerance mechanisms on suppressing 2F5 mAb heavy chain-expressing B cells, and is similar to that seen in other knock-in strains expressing Ig heavy chains of autoreactive antibodies. This mouse strain will be useful for developing immunization strategies to circumvent tolerance mechanisms and safely induce broadly neutralizing antibodies against the gp41 membrane proximal external region.
Supported by a Collaboration for AIDS Vaccine Discovery grant from the Bill and Melinda Gates Foundation, NIH, NIAID, DAIDS grant AI0678501 and the Duke Center For AIDS Research.